1. Field of the Invention
The present invention relates generally to an electromagnetic machine for converting mechanical energy into electrical energy and vice versa. In particular, the present invention relates to a reciprocating linear electromagnetic machine comprising a stator, a coil mounted in the stator for generating magnetic flux, and a plunger having a plurality of magnetic segments dispose axially and of alternating polarity arranged for reciprocation with respect to the stator. The present invention also relates to the invention of the copending patent application of Suresh K. Bhate and Nicholas G. Vitale, entitled "A Monocoil Reciprocating permanent Magnet Electric Machine With Self Centering Force", Ser. No. 835,957, filed Mar. 4, 1986, and assigned to the same assignee as the present invention, now U.S. Pat. No. 4,827,163.
2. Description of the Prior Art
Linear electromagnetic machines are known which comprise a stator having a plurality of axially spaced coils for generating a magnetic flux and a permanent magnet plunger reciprocating with respect to the stator. Examples of such machines are found in U.S. Pat. Nos. 4,349,757 to Bhate and 4,454,426 to Benson. A machine employing a single coil mounted in the stator is found in the foregoing referenced copending patent application.
In the Bhate patent No. 4,349,757 the magnets are of equal axial lengths with alternately oriented radial polarities and are spaced apart axially on centers equal to the corresponding spacing between the coils in the patent to, Benson No. 4,454,426 the machine is designed so that all magnetic segments are of equal axial length and are disposed at intervals of one-half the center to center spacing of the coils (see col. 6, lines 39-43). Such machines generally exhibit higher inductance and a lower power factor than is desired for most applications necessitating the need to provide for external power factor correction means which increases the cost of the machine. Machine designs exhibiting lower inductance and higher power factor require a large amount of permanent magnet material resulting in a machine which is too expensive for most commercial applications.
Accordingly, it would be very desirable to provide a linear electromagnetic machine with lower inductance and a higher power factor while at the same time not requiring a large increase in the amount of magnetic material.
In the foregoing referenced copending patent application a plunger having permanent magnet segments is arranged for linear reciprocation with respect to a stator having axially spaced-apart pole pieces and an electric coil for generating magnetic flux. The plunger has first and second axially spaced-apart outer permanent magnet segments provided at its respective ends. The plunger also has first and second axially spaced-apart inner permanent magnet segments provided at its respective ends and axially inward of the outer magnet segments. The first and second outer magnet segments are both magnetized radially in the same direction, while the first and second inner magnet segments are also each magnetized in the same direction but which direction is opposite that of the outer magnet segments. In operation, an outer magnet segment interacts with one stator pole piece while an inner magnet segment simultaneously interacts with the other axially spaced pole piece. For example, for a first extreme axial position of the plunger the first outer magnet segment would be adjacent one stator pole piece while the second inner magnet segment would be adjacent the other pole piece which is axially spaced from the one pole piece. Similarly, in the other extreme axial position of the plunger the second outer magnet segment would be adjacent that one pole piece while the first inner magnet segment would be adjacent the other stator pole piece.